High-speed image sensors have been widely used in many applications in different fields including the automotive field, the machine vision field, and the field of professional video photography. Some applications in these fields require the detection and capture of LED lights, which has proven to be difficult. For example, automotive image sensors face the problem of LED flickering. Future automotive vehicle lights, traffic lights and signs will include LED that is pulsed at 90-300 Hz with high peak light intensity. This requires that the minimum exposure time be kept over 10 ms. A very high full well capacity or very low light intensity are thus needed to avoid pixels to get saturated and lose useful information.
Current solutions to address the overflow and loss of useful information from saturated pixels include enhancing the full well capacity with a lateral overflow integrating capacitor (LOFIC). When the photodiode is filled after reaching a corresponding FWC, the excess charge is leaked into a floating drain. A large capacitor connected to the floating drain can then store the excess charge. However, the maximum full well capacity is thus limited by the floating drain capacitor rather than the photodiode full well capacity. Other solutions involve using non-linear sensor (e.g., logarithmic sensors) to enlarge the full well capacity, or using split diode pixels or subpixel sensors to maintain minimum exposure time by minimizing sensitivity of small photodiode.
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